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 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The electrochemical detection of H2O2 was investigated on a cobalt oxide nanoparticles modified glassy carbon electrode in phosphate buffer solution (pH 7). Cyclic voltammetry at potential range -1.1 to 1.1 V from CoCl2 natural aqueous solution produced well defined cobalt oxide nanoparticles deposited on the surface of glassy carbon electrode. The surface of resulting electrode was characterized with SEM. The formation of cobalt oxyhydroxide film was investigated by cyclic voltammetry in alkaline and natural aqueous solution. The modified electrode showed well defined and stable redox couples in both alkaline and natural aqueous solution. The modified electrode showed excellent electrocatalytic activity for oxidation of hydrogen peroxide. The response to H2O2 on the modified electrode was examined using cyclic voltammetry and amperometry. The amperometric detection of hydrogen peroxide is carried out at 0.75 V versus Ag/AgCl reference electrode in phosphate buffer solution with pH 7.4. The detection limit (S/N=3) was 0.4 nM with linearity up to 6 orders of magnitude and sensitivity of 4.86 microA microM(-1) cm(-2). The response time of the electrode to achieve 95% of the steady-state current is <2 s. No measurable reduction in analytical performance of the modified electrode was found by storing the electrode in ambient conditions for 20 days. This modified electrode recedes many advantages such as remarkable catalytic activity, good reproducibility, simple preparation procedure and long term stability of signal response during hydrogen peroxide oxidation. The immobilization of cobalt oxide nanoparticles on the surface of GC electrode appears to be a highly efficient method for the development of a new class of sensitive, stable and reproducible hydrogen peroxide electrochemical sensor.
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PMID:Nanomolar detection of hydrogen peroxide on glassy carbon electrode modified with electrodeposited cobalt oxide nanoparticles. 1756 Mar 81

The bactericidal process of Ag/Al2O3 to Escherichia coli has been investigated to clarify the bactericidal mechanism. In SEM images, the configuration of E. coli cells contacting with the catalyst surface was quite different from that contacting with AgNO3 solution, which indicated that the Ag+ eluted from the catalyst did not play an important role in the bactericidal process. The bactericidal experiments strongly confirmed the contribution of multiform reactive oxygen species (ROS) (super oxide dismutase (SOD) and catalase as the scavengers for O2*- and H2O2, respectively) to bactericidal effect on the catalyst surface. Furthermore, the surface modification of Ag/Al2O3 by ultraviolet and formaldehyde influenced the bactericidal effect obviously, which not only confirmed the bactericidal mechanism of catalytic oxidation but also provided evidence for the synergistic effect between Ag and Al2O3 on the catalyst surface.
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PMID:Bactericidal mechanism of Ag/Al2O3 against Escherichia coli. 1790 10

This study evaluated the morphological effects produced in vivo by two in-office bleaching agents on enamel surface roughness using a noncontact profilometric analysis of epoxy replicas. The null hypothesis tested was that there would be no difference in the micromorphology of the enamel surface during or after bleaching with two different bleaching agents. Eighteen subjects were selected and randomly assigned to two treatment groups (n=9). The tooth whitening materials tested were 38% hydrogen peroxide (HP) (Opalescence Xtra Boost) and 35% carbamide peroxide (CP) (Rembrandt Quik Start). The bleaching agents were applied in accordance with manufacturer protocols. The treatments were repeated four times at one-week intervals. High precision impressions of the upper right incisor were taken at baseline as the control (CTRL) and after each bleaching treatment (T0: first application, T1: second application at one week, T2: third application at two weeks and T3: fourth application at three weeks). Epoxy resin replicas were poured from impressions, and the surface roughness was analyzed by means of a non-contact profilometer (Talysurf CLI 1000). Epoxy replicas were then observed using SEM. All data were statistically analyzed using ANOVA and differences were determined with a t-test. No significant differences in surface roughness were found on enamel replicas using either 38% hydrogen peroxide or 35% carbamide peroxide in vivo. This in vivo study supports the null hypothesis that two in-office bleaching agents, with either a high concentration of hydrogen or carbamide peroxide, do not alter enamel surface roughness, even after multiple applications.
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PMID:Effect of two in-office whitening agents on the enamel surface in vivo: a morphological and non-contact profilometric study. 1843 85

A novel method for duplicating the hierarchical structures of biological substances at nanometer resolution in manganese oxides has been developed. This innovation uses natural biomorphic specimens, such as butterfly wing, cotton, and wood as templates. The biotemplates were first treated with either HCl/NaOH or HCl/H2O2/NaOH and then mixed with an aqueous solution of KMnO4. The treated biological materials were then ultrasonically irradiated, and finally, the biological templates were removed by calcination in air at temperatures between 500 and 800 degrees C. The structures of the resulting manganese oxides were characterized by a combination of XRD, FE-SEM, TEM and EDS. It was found that the fine hierarchical structures of the biological templates down to the nanometer scale were faithfully duplicated, and the duplication was positive. A mechanism for the positive replication is proposed and discussed in terms of the effects of the sonochemical reaction as well as the surface modification prior to the sonochemical reaction. The same sonochemical method can be extended to the duplication of intricate hierarchical structures of other biological forms in a large range of metal oxides.
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PMID:Precision replication of hierarchical biological structures by metal oxides using a sonochemical method. 1848 91

A comparison of different purification procedures for single walled carbon nanotubes (SWCNTs) synthesized by laser-vapourization has been presented. The methods involved gas-phase oxidation by calcination, liquid-phase oxidation by H2O2, hydrothermal treatment and acid refluxing in HCI. Sample purity is documented with Raman spectroscopy, Transmission electron microscopy, Scanning electron microscopy and thermogravimetric analysis. Multi-spot analyses were done to check the homogeneity of the purified samples. Different purification processes produced SWCNT material with purity in the range of 48-78%. Raman and TEM results suggested that prolonged calcination results in selective etching of larger diameter nanotubes. SEM and TGA analyses showed increase in density of SWCNTs with better oxidation resistance after purification.
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PMID:Purification of laser synthesized SWCNTs by different methods: a comparative study. 1919 41

The aim of this study was to evaluate in vitro the effect of different in-office bleaching systems on the surface morphology of bovine dentin. Thirty tooth fragments measuring 4 x 4mm, containing enamel and dentin, were obtained from the crowns of extracted bovine incisors. Samples were subjected to simulated intracoronal bleaching techniques using conventional (Opalescence Endo and Whiteness Super Endo) and light-activated systems (Opalescence Xtra) and Whiteness HP Maxx). Controls were treated with either sodium perborate mixed with 10% hydrogen peroxide or no bleaching agent. The samples were observed under SEM and the recorded images were evaluated for topographic alterations. The ultrastructural alterations of dentin observed in this study varied greatly between groups according to the products used. Higher pH products (Whiteness HP Maxx) and Opalescence Xtra) associated with in-office techniques yielded better maintenance of dentin ultrastructure. Apparently, both low pH and hydrogen peroxide oxidation play a role in altering the ultrastructure of dentin during internal dental bleaching. The use of alkaline products with reduced time of application (in-office techniques) may decrease such morphological alterations.
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PMID:Effect of different bleaching systems on the ultrastructure of bovine dentin. 1929 Aug 96

This work studied the dissolution of uranium dioxide and precipitation characteristics of uranyl ions in alkaline and acidic solutions depending on the presence of carbonate ions and H2O2 in the solutions at different pHs controlled by adding HNO3 or NaOH in the solution. The chemical structures of the precipitates generated in different conditions were evaluated and compared by using XRD, SEM, TG-DT, and IR analyses together. The sizes and forms of the precipitates in the solutions were evaluated, as well. The uranyl ions were precipitated in the various forms, depending on the solution pH and the presences of hydrogen peroxide and carbonate ions in the solution. In a 0.5 M Na2CO3 solution with H2O2, where the uranyl ions formed mixed uranyl peroxy-carbonato complexes, the uranyl ions were precipitated as a uranium peroxide of UO4(H20)4 at pH 3-4, and precipitated as a clarkeite of Na2U2Ox(OH)y(H2O)z above pH 13. In the same carbonate solution without H2O2, where the uranyl ions formed uranyl tris-carbonato complex, the uranyl ions were observed to be precipitated as a different form of clarkeite above pH 13. The precipitate of uranyl ions in a nitrate solution without carbonate ions and H2O2 at a high pH were studied together to compare the precipitate forms in the carbonate solutions.
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PMID:Precipitation characteristics of uranyl ions at different pHs depending on the presence of carbonate ions and hydrogen peroxide. 1945 86

Printed circuit board wastewater typically contains organics and metal ions. The study explored the feasibility of a sequential procedure, FFP (the combination of the Fenton method and the Ferrite process), for treating printed circuit board wastewater, and established the optimum parameters for it. The analytical results showed that the proper pH level was 2 for Fenton oxidation, and the appropriate H2O2 dosing type was batch dosing. For the Ferrite process, the suitable Fe/M (Fe is the total dose of Fe2+ added to a solution and M is the initial total moles of various metal ions in untreated wastewater) molar ratio was 10 and the sludge met the toxicity characteristic leaching procedure (TCLP) standards. Following FFP treatment, effluent water or sludge easily met Taiwan's standards. Finally, the SEM/EDS test demonstrated that particle sizes of the sludge were approximately 50-80 nm, and the saturation magnetization was 67.5 emu/g.
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PMID:Treatment of printed circuit board industrial wastewater by Ferrite process combined with Fenton method. 1949 13

In this study the new catalyst Si-FeOOH was synthesized by adding Si to the traditional FeOOH and the mechanic strength of this new catalyst could be enhanced greatly. The photo-degradation of dimethyl phthalate (DMP) by UV/Si-FeOOH/H2O2 was investigated. The new catalyst Si-FeOOH was amorphous structure with high surface area and low soluble iron by XRD, IR and SEM. The efficiency of DMP degradation by UV/Si-FeOOH/H2O2 could reach 97% after 30 min reaction time at pH 5, 0.5 g/L dosage of Si-FeOOH, and 2.0 mmol/L of H2O2 under 125W UV365 irradiation. DMP could be degraded effectively by synergistic effect of UV, Si-FeOOH and H2O2. The Si-FeOOH photocatalyst can be very easily recovered and its catalytic activity also remained after several rounds of reaction.
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PMID:[Degradation of dimethyl phthalate (DMP) in aqueous solution by UV/Si-FeOOH/H2O2]. 2107 26

Polythiophene/poly(sodium 4-styrene sulfonate) (PT/PSS) composite nanoparticles having different particle size were prepared by Fe(3+)-catalyzed oxidative polymerization in aqueous medium. This facile method includes a FeCl3/H2O2 (catalyst/oxidant) combination system, which guarantees a high conversion (more than 95%) of thiophene monomers in various concentration of poly(styrene sulfonate) (PSS) with only a trace of FeCl3. Particle size of PT/PSS composite nanoparticles decreased from 134 nm to 26 nm as the concentration of PSS and H2O2 increased, and which was confirmed by SEM and CHDF analyses. The poly(ethylene terephthalate) (PET) film coated with PT/PSS was transparent and showed a high conductivity in a dried state. The sheet resistivity decreased as the ratio of PT to PSS increased. Photoluminescence property of the PT/PSS composite nanoparticles was also investigated.
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PMID:PSS resin-fortified polythiophene nanoparticles for highly transparent conducting films. 2113 30


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